With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
Ever since the institute of electrical and electronics engineers (IEEE) 802, i.e., a standardization organization for WLAN technologies, was established in February 1980, many standardization works have been conducted. In the initial WLAN technology, a frequency of 2.4 GHz was used according to the IEEE 802.11 to support a data rate of 1 to 2 Mbps by using frequency hopping, spread spectrum, infrared communication, etc. Recently, the WLAN technology can support a data rate of up to 54 Mbps by using orthogonal frequency division multiplex (OFDM). In addition, the IEEE 802.11 is developing or commercializing standards of various technologies such as quality of service (QoS) improvement, access point protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environments, fast roaming, mesh networks, inter-working with external networks, wireless network management, etc. The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network.
The IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to 540 Mbps or higher, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate. In addition, this standard may use a coding scheme which transmits several duplicate copies to increase data reliability and also may use the OFDM to support a higher data rate.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. However, an IEEE 802.11n medium access control (MAC)/physical layer (PHY) protocol is not effective to provide a throughput of 1 Gbps or higher. This is because the IEEE 802.11n MAC/PHY protocol is designed for an operation of a single station (STA), that is, an STA having one network interface card (NIC), and thus when a frame throughput is increased while conforming to the conventional IEEE 802.11n MAC/PHY protocol, a resultant additional overhead is also increased. Consequently, there is a limitation in increasing a throughput of a wireless communication network while conforming to the conventional IEEE 802.11n MAC/PHY protocol, that is, a single STA architecture.
Therefore, to achieve a data processing rate of 1 Gbps or higher in the wireless communication system, a new system different from the conventional IEEE 802.11n MAC/PHY protocol (i.e., the single STA architecture) is required. A very high throughput (VHT) WLAN system is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of 1 Gbps or higher in a MAC service access point (SAP).
The VHT WLAN system allows simultaneous channel access of a plurality of VHT non-AP STAs for the effective use of a radio channel. For this, a multi-user multiple input multiple output (MU-MIMO)-based transmission using multiple antennas is supported. A VHT access point (AP) can concurrently transmit spatial-multiplexed data to a plurality of VHT non-AP STAs. When data is concurrently transmitted by distributing a plurality of spatial streams to the plurality of non-AP STA through a plurality of antennas, an overall throughput of the WLAN system can be increased.
In the WLAN system, the non-AP STA performs scanning, authentication, and association procedures on an AP that provides a service. If a plurality of APs are found as a result of AP scanning performed by the non-AP STA, the non-AP STA can select an AP to be associated. In this case, load balancing of an overall network is preferably taken into account when the non-AP STA selects the AP.
A plurality of APs are installed as WLAN terminals are widespread and its utilization is increased. Accordingly, an overlapping basic service set (OBSS) environment increases in which a basic service area (BSA) of a basic service set (BSS) using the same channel overlaps either partly or wholly. In addition, in case of a WLAN supporting MU-MIMO, there may be more considerations when selecting an AP to be associated with a non-AP STA. Therefore, it may be very important to provide the non-AP STA with information that can be used in a process of selecting the AP to be associated with the non-AP STA in terms of managing overall efficiency of the WLAN.
In order to increase the overall efficiency of the WLAN, there is a need for a method for generating control information that can be used by a non-AP STA when selecting an AP to be associated with the non-AP STA and for transmitting the control information to the non-AP STA and also a method for selecting the AP by the non-AP STA on the basis of the control information.